CZĘSTOCHOWA UNIVERSITY OF TECHNOLOGY FACULTY OF MATERIALS PROCESSING TECHNOLOGY AND APPLIED PHISICS Department of Industrial Furnances and Environmental Protection PRECISE MEASUREMENTS OF THE SURFACE TEMPERATURE OF SOLID BODIESPRECISE MEASUREMENTS OF THE SURFACE TEMPERATURE OF SOLID BODIES Author: mgr inż. Agnieszka Klos

Introduction The heating of metal charge before hot plastic working is a very important process which influences both the quality of rolled product and the costs of processing. The heating of metal charge before hot plastic working is a very important process which influences both the quality of rolled product and the costs of processing. In a properly conducted technological process, following the charge heating programme should assure the proper quality of the process, that is prepare the charge at the specific temperature and with permissible temperature differences. In the case of heat treatment, temperature differences on the surface are also important.

In industrial furnaces, the continuous measurement of charge surface temperature is very difficult, or even impossible. There is no method for controlling the charge surface temperature during the heating process. We presume that this control method can be provided in the future by computer-aided measurement using digital photopyrometry. Research into such measurements are being conducted at the Department of Industrial Furnaces and Environmental Protection of the Czestochowa University of Technology.

Digital photopyrometry Digital photopyrometry is a contact-less method. The measurement and recording of temperature is done using a digital camera. The method consists in making a photograph of the radiating object under examination. The digital photograph is transformed in greyscale image. Such transformation enables the temperature of the examined object to be represented as a funkction of the absolute greyscale level.

The digital pictures exemple

Measurement methodology Tests were carried out on a steel sample. The sample was heated directly in the chamber of an electric & gas furnace with a precise temperature control capability. The reference sample temperature was measured with an Ni- CrNi thermocouple with the simultaneous photographic recording of the image of the test sample. Using the obtained image, the readout of the temperature being measured was done with two methods. The first method was by manual reading out the average greyscale level of for the assumed surface. The value of the greyscale level readout was then converted into the temperature value. In the second method, the temperature value was also read out directly using a developed computational program.

t0t0 t=f(r) Number photo Value t 0 o C Value rValue t 1 o C

It has been established that the effect of temperature on the greyscale level can be described with the following equation: where: a, b, c, d – constant value, r – degree greyss, t – temperature, °C. The values of the constants in relationship (1) were established by using the results of measurements carried out for developing the correlation between the temperature value and the greyscale level. Thus, relationship (1) for S=1/60s was obtained in the form, as below: (1) (2)

Comparison of thermovision and digital photopyrometry Measurement results obtained by three different methods are shown on the graph. The temperature values obtained using the digital camera differ from the reference temperatures to a considerably lesser extent compared with the temperature values measured with the thermovision camera. Results of temperature measurements with utilization of three method In the case of the digital camera, a larger error is observable at lower temperatures. By contrast, for the thermovision camera, the error increases with the increase in specimen temperature.

The masuring precise of digital photopyrometry The diagram is presented the precise of temperature readout from a digital picture manuallyand from using the developed computer program. The diagram is presented the precise of temperature readout from a digital picture manually and from using the developed computer program. The accuracy of temperature readout from a digital picture manually by reading out the average greyscale level is placed at a measuring error level of 3-4%.This error is greater for lower temperatures. Whereas, the measuring error for temperature read out using the developed computer program is approx. 1%, which is indicative of high accuracy of this measurement method.

The temperature characteristic for different solid bodies The digital photopyrometry can be used to measurement of temperature different solid bodies. For the comparision were carry out the measurement for some materials. The temperature characteristic for chamotte, steel and graphite are shown on the diagram.

Summary The analysis of measurement results shows that the results of temperature measurement using a digital camera are taken with high accuracy. In addition, the use of a suitable computer program enables a considerable automation of the process and facilitates reading out, while enhancing the accuracy of temperature readout (measurement). By using the program, the punctual read out of steel and the other materials surface temperature is possible.

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